The present invention relates generally to a chip carrier having a taught and planar nozzle plate with a nozzle having a true bore formed therein. More specifically, the present invention relates to a chip carrier having a taught and planar nozzle plate with a nozzle that has a nozzle camber angle that is aligned with a firing axis of a thermal ink jet resistor and a nozzle axis of the nozzle so that fluid injected into the nozzle exits in a direction along the nozzle axis.
Articles and publications set forth herein are presented for the information contained therein: none of the information is admitted to be statutory xe2x80x9cprior artxe2x80x9d and we reserve the right to establish prior inventorship with respect to any such information.
Ink jet drop directionality can be improved by providing a nozzle plate having a nozzle with a true bore. A true bore is simply a nozzle in the nozzle plate that has sidewall surfaces that are uniform and symmetric about an axis of the nozzle. By way of analogy, an example of a true bore is the barrel of a cannon. The cannon has barrel sidewalls that are symmetric with respect to a bore axis of the canon. Thus, a projectile propelled thru the barrel exits the barrel with a trajectory that is along the bore axis. On the other hand, if the barrel has sidewalls that are not symmetric with respect to the bore axis then the barrel will not have a true bore (i.e. a crooked barrel) and the projectile will exit the barrel with a trajectory that is not along the bore axis. Consequently, the projectile will not strike its desired impact point. Therefore, lack of a true bore results in inaccuracies in the trajectory of the projectile.
Similarly, for a thermal ink jet printhead, an ink drop ejected from a firing chamber of the printhead and into a nozzle that does not have a true bore results in the ink drop exiting the nozzle with a trajectory that is not along the nozzle axis. As a result, the ink drop trajectory will deviate from a desired impact point on a print media such as a sheet of paper positioned opposite the nozzle.
In a typical thermal ink jet printhead, a semiconductor substrate is bonded to an orifice plate (a nozzle plate) using a barrier layer. A firing chamber is formed by the substrate and the barrier layer. A firing element such as a thermal ink jet resistor is disposed in the firing chamber and a firing axis of the firing element is aligned with a nozzle axis of a nozzle formed in the nozzle plate. The barrier layer seals the firing chamber to the nozzle plate so that the firing chamber is in fluid communication with the nozzle. A fluid channel communicates ink from an ink reservoir to the firing chamber. The substrate includes a signal line that electrically communicates a signal from a control unit (which may be connected to a source of printing data) to the firing element. A signal communicated to the firing element causes ink disposed on the element to be heated and subsequently ejected from the firing chamber and into the nozzle. The ink drop exits the nozzle with a trajectory that is determined by the symmetry of the nozzle. If the nozzle has a true bore, then the trajectory of the ink drop is substantially along an axis of the nozzle. Conversely, if the nozzle does not have a true bore then the trajectory of the ink drop deviates from the nozzle axis. By way of example, a general discussion of thermal ink jet printheads, nozzle plates, and thermal ink jet printhead construction can be found in the Hewlett-Packard Journal, Volume 39, No. 5, October 1998, Volume 39, No. 4, August 1998, and Volume 36, No. 5, May 1985.
Prior attempts to create a nozzle plate with a true bore nozzle have been frustrated by deformities in the nozzle plate. Typically, the nozzle plate is a thin film of flexible material such as a polyimide film, for example. The nozzle plate has opposed input and output surfaces thru which an orifice (a nozzle) is formed. The nozzle plate is then bonded to the substrate in a process called staking where the barrier layer is applied to the substrate and then heat and pressure are applied to attach the input surface of the nozzle plate to the barrier layer. The completed assembly is then baked at a high temperature to cure the barrier layer.
The deformities in the nozzle plate aries due to compressive buckling of the nozzle plate caused by the staking and baking process. Resulting is dimpling of the nozzle plate. The dimples in the nozzle plate resemble the peaks and troughs of ocean waves and can be sinusoidal in appearance. Therefore, the input and output surfaces of the nozzle plate deviate from planarity such that a nozzle formed in the nozzle plate will not have sidewall surfaces that are symmetric about the nozzle axis.
Moreover, the nozzle has openings on the input and output surfaces. A center point of symmetry on an input side of the nozzle is not coaxially aligned with a center point of symmetry on an output side of the nozzle. Resulting is misalignment between the input and output sides of the nozzle with respect to the nozzle axis. Because of the misalignment, sidewall surfaces of the nozzle are not symmetric with the nozzle axis, therefore, the nozzle does not have a true bore.
Referring to FIG. 1, there is illustrated a dimpled nozzle plate 101 having an input surface 103 disposed opposite an output surface 105. The opposed surfaces have a generally sinusoidal contour; however, the nozzle plate can have other surface deformations that can result in a nozzle that does not have a true bore. A nozzle 107 is formed in the nozzle plate 101 by sidewall surfaces 109 that extend between the input surface 103 and the output surface 105. Those skilled in the ink jet printer art commonly refer to the nozzle plate 101 as an orifice plate and the nozzle 107 as an orifice; however the term nozzle plate and nozzle will be used hereinafter.
A center point of symmetry 111 on an input side 113 (the side from which ink or some other fluid is injected into the nozzle) of the nozzle 107 is not coaxially aligned with a center point of symmetry 115 on an output side 117 of the nozzle 107. A nozzle axis 119 is referenced to the center point of symmetry 111 on the input side 113. Deviation from coaxial alignment between the center points of symmetry is measured in angular degrees by a nozzle camber angle (NCA) 123. The NCA 123 is measured between the nozzle axis 119 and a camber line 121 extending thru the center points of symmetry 111 and 115 respectively. An ink drop or other fluid (not shown) entering the input side 113 of the nozzle 107 will exit the output side 117 with a trajectory that substantially matches the NCA 123 (i.e. the fluid trajectory is along the camber line 121). Because of the dimple in the nozzle plate 101, the sidewall surfaces 109 are not symmetric with respect to the nozzle axis 119 as will be discussed below.
Consequently, the ink drop, for example, will not strike a desired impact point on a print media. FIG. 2 is an illustration of the effect the dimpled nozzle plate 101 of FIG. 1 has on ink drop directionality. A print surface 133 of a print media 131 is shown with a desired impact point X and an actual impact point Xxe2x80x2 displaced a lateral distance from the desired impact point X. The print media 131 can be a sheet of paper, for example. As can be seen in FIG. 2 the actual impact point Xxe2x80x2 coincides with the camber line 121 and is caused by the ink drop (not shown) having a trajectory that substantially matches the NCA 123.
Additionally, the sidewall surfaces 109 of the nozzle 107 are not symmetric about the nozzle axis 119 due to the dimpling of the nozzle plate. Lack of symmetry between the nozzle axis 119 and the sidewall surfaces 109 is shown by unequal length radius lines d1 and d1xe2x80x2, d2 and d2xe2x80x2, and d3 and d3xe2x80x2 that extend between the nozzle axis 119 and the sidewall surfaces 109. Essentially, the nozzle 107 does not have a true bore due to lack of symmetry between the sidewall surfaces 109 and the nozzle axis 119.
Accordingly, the center point of symmetry 115 on the output side 117 is not coaxially aligned with the nozzle axis 119 as shown in FIG. 2a. The center point of symmetry 115 on the output side 117 is illustrated as a cross xe2x80x9c+xe2x80x9d and the nozzle axis 119 is illustrated as a dot xe2x80x9cxe2x80xa2xe2x80x9d in FIG. 2a. 
Ideally, however, it is desirable to have the center point of symmetry 115 on the output side 117 to be coaxially aligned with the nozzle axis 119 as shown in FIGS. 3 and 3a. As can be seen in FIG. 3, the center point of symmetry 115 on the output side 117 is coaxially aligned with the center point of symmetry 111 on the input side 113 so that the camber line 121 is coaxially aligned with the nozzle axis 119 and the NCA 123 is substantially 0.0 degrees. Resulting is an ink drop (not shown) that strikes the print side 133 of the print media 131 at the desired impact point X. Essentially the true bore of the nozzle 107 results in the camber line 121 coinciding with the desired impact point X.
Moreover, the sidewall surfaces 109 of the nozzle 107 are symmetrically disposed about the nozzle axis 119 such that the radius lines d1 and d1xe2x80x2, d2 and d2xe2x80x2, and d3 and d3xe2x80x2 are of equal length. Therefore, as can be seen in FIG. 3a, the center point of symmetry 115 on the output side 117 is coaxially aligned with the nozzle axis 119. Another way of viewing FIGS. 3 and 3a is that coaxial alignment of the center point of symmetry 115 on the output side 117 with the center point of symmetry 113 on the input side 113 results in coaxial alignment of the NCA 123 with the nozzle axis 119, whereby the nozzle 107 has a true bore.
FIG. 4 is an illustration of the dimpled nozzle plate 101 coupled to a substrate 300 that defines an ink jet print head 301 mounted to the input side 103 of the nozzle plate 101 by a barrier layer 303. A firing chamber 305 is formed in the barrier layer 303 and the substrate 300. The barrier layer 303 seals the firing chamber 305 to the nozzle plate 101 so that the firing chamber 305 is in fluid communication with the nozzle 107. A fluid channel 307 supplies ink (not shown) to the firing chamber 305 from an ink reservoir (not shown). The firing chamber 305 includes a firing element 309 disposed in the firing chamber 305 and having a firing axis 311 that is aligned with the nozzle axis 119. A signal line 315 connects the firing element 309 to a control unit (not shown) that electrically communicates a signal to the firing element 309. Those skilled in the ink jet printer art commonly refer to the firing element 309 as a thermal ink jet resistor; however, the term firing element will be used hereinafter.
As mentioned previously, the firing element 309 is operative to heat ink supplied to the firing chamber 305 into an ink bubble 313 that is ejected from the firing chamber 305 along the firing axis 311. The ink bubble 313 enters the input side 113 of the nozzle 107 and exits the nozzle 107 thru the output side 117. As can be seen in FIG. 4, due to dimpling of the nozzle plate 101 the NCA 123 is not aligned with the nozzle axis 119, therefore, the ink drop 213 will have a trajectory that substantially matches the NCA 123. Resulting is inaccuracy in the directionality of the ink drop 313 such that the ink drop 313 travels along the camber line 121 rather than the nozzle axis 119.
Although FIG. 4 shows dimple on the output surface 105, the input surface 103 may also be dimpled. Dimpling of the input surface 103 can cause additional problems, namely, a defective fluid seal between printhead 301 and the nozzle plate 101 caused by voids in the barrier layer 303. The ink drop 313 can be diverted into those voids resulting in reduced ink drop output, a clogged nozzle, or a defective firing chamber. Accordingly, it is important that both the input surface 103 and output surface 105 be planar surfaces that are parallel to each other.
Therefore, there is a need to overcome the disadvantages associated with dimpling of the nozzle plate and the resulting inaccuracies in ink drop directionality. A nozzle plate that is taught and has planar input and output surfaces can eliminate the dimpling of the nozzle plate. Furthermore, the planar surfaces of the nozzle plate result in the input and output surfaces being parallel to each other. The taught nozzle plate provides a surface thru which a true bore nozzle can be formed and provides a flat and stable surface for mounting the ink jet printhead to the nozzle plate.
Moreover, there is a need for a nozzle plate that remains taught and maintains planarity of the input and output surfaces after the nozzle plate has been subjected to the staking and baking process.
Another disadvantage to mounting the ink jet printhead to the nozzle plate is that the signal lines in the printhead must be connected to a control unit that communicates print signals to the printhead. In a typical application, the nozzle plate includes electrically conductive traces that are disposed on the input or output surfaces. The traces connect to a bonding pad or similar structure on the printhead and are operative to communicate signals from the control unit to the signal lines connected to the firing element. The traces can be patterned on the nozzle plate using PC board lithography techniques, for example. Alternatively, wire bonds can be used to facilitate connection of the control unit to the signal lines. One or more apertures are formed in the nozzle plate to facilitate routing of the trace or the wire bond to the printhead.
Thus, the nozzle plate may need to be made larger in order to accommodate the traces and apertures. It is more difficult to prevent surface irregularities in a nozzle plate that serves dual roles as both a fluidic device and an electronic device, mainly due to the larger area of the nozzle plate and defects introduced by processing steps related to making the necessary electrical connections to the printhead.
Therefore, there is a need to overcome the disadvantages associated with combining the fluidic and electronic functions in the nozzle plate. A carrier frame operative to support the nozzle plate so that the printhead can be mounted to the nozzle plate without electrical connections can decouple the fluidic and electronic functions of the nozzle plate. A separate flexible circuit material can be connected to the carrier frame and can communicate electrical signals between the control unit and the printhead. Separation of the electronic and fluidic functions has the added advantage of allowing the nozzle plate and the flex circuit to be made from different materials.
The problems and limitations associated with dimpling of the nozzle plate are addressed by various aspects of the present invention. Dimpling of the nozzle plate is eliminated by disposing the nozzle plate on a carrier frame and staking and baking the nozzle plate to the carrier frame so that the nozzle plate is taught, planar, and has input and output surfaces that are parallel to each other. After the staking and baking process the nozzle plate remains taught and planar so that nozzles formed in the nozzle plate have a true bore. The carrier frame and the nozzle plate define a chip carrier. An ink jet printhead is mounted to an input surface of the nozzle plate.
Additionally, the problems associated with a nozzle plate that performs both fluidic and electronic functions is solved by using the above mentioned chip carrier and including an electrically conductive bonding pad on the carrier frame. A separate flex circuit that carries electrically conductive traces is mounted to the carrier frame and the traces are connected to the bonding pads on the carrier frame. Signal lines on an ink jet printhead mounted to the nozzle plate can be connected to the bonding pads thereby decoupling the fluidic function of the nozzle plate from the electronic function of the traces. The flex circuit and the nozzle plate need not be made from the same material. For instance, the nozzle plate can be made from a material capable of forming a taught nozzle plate and the flex circuit can be made from a material that is well suited for patterning and etching of signal lines.
Broadly, the present invention provides a chip carrier that includes a carrier frame having opposed shelf and base surfaces, a frame aperture extending between the shelf and base surfaces, and a nozzle plate having opposed input and output surfaces. A nozzle is formed by sidewall surfaces that extend between the opposed surfaces. The nozzle plate is fixedly disposed on the shelf surface of the carrier frame with the input surface adjacent to the frame aperture. The nozzle plate is characterized by being disposed on the shelf surface in a state of tensile stress so that the input and output surfaces are taught, planar, and parallel to each other.
The tensile stress on the nozzle plate is operative to symmetrically dispose the sidewall surfaces of the nozzle with respect to a nozzle axis so that the nozzle has a true bore and a nozzle camber angle is coaxially aligned with a nozzle axis. A fluid injected into the nozzle exits the nozzle with a trajectory that substantially matches the nozzle camber angle.
In one embodiment of the present invention, the nozzle plate is made from a first material that has a first thermal expansion coefficient and the carrier frame is made from a second material that has a second thermal expansion coefficient. The second thermal expansion coefficient is less than the first thermal expansion coefficient so that the dissimilarity between the first and second thermal expansion coefficients operates to generate the tensile stress on the nozzle plate.
In another embodiment of the present invention, the nozzle has converging sidewall surfaces that converge in a direction toward an output side of the nozzle. In one embodiment the converging sidewall surfaces are arcuate in shape.
In one embodiment of the present invention, the nozzle plate is fixedly .connected to the shelf surface of the carrier frame by an adhesive disposed between the shelf surface and the input surface of the nozzle plate.
In another embodiment of the present invention, the shelf surface includes a raised portion defining a lip that extends outward of the shelf surface and terminates in a planar upper surface. The input surface of the nozzle plate is disposed on the upper surface of the lip and the nozzle plate is fixedly connected to the shelf surface by an adhesive disposed between the shelf surface and the input surface of the nozzle plate. The lip provides a flat reference plane upon which to mount the nozzle plate so that planarity of the nozzle plate is not compromised by non-uniform thickness of the adhesive.
In one embodiment of the present invention, a barrier layer mounts an ink jet printhead to the input surface of the nozzle plate. A firing chamber of the printhead is aligned with and is in fluid communication with a nozzle in the nozzle plate. The firing chamber includes a firing element that has a firing axis that is coaxially aligned with the nozzle axis.
In another embodiment of the present invention, the nozzle plate includes at least one feed-thru aperture for routing an interconnect line from a bonding pad disposed on the carrier frame to a signal line on the ink jet printhead.
In one embodiment of the present invention, the chip carrier is mounted to a flex circuit that includes an electrically conductive trace. The trace connects to a bonding pad disposed on the carrier frame. The bond pad is in electrical communication with the signal line in the ink jet printhead. The trace is operative to communicate a signal from the control unit to the signal line.